As the initial reaction dies down, it's worth considering how this happened, what it means, and what might come next. The invaluable Axios news site has some noteworthy insights on the latter problem that I will get to shortly.

I am convinced it was a mistake to withdraw. In this I share the view of many current and former business leaders, including the Secretary of State, that the US was better off as a party to the deal and all the future negotiations it entails. Even if the goal was truly to renegotiate the agreement on more favorable terms, signaling withdrawal first seems counterproductive. However, I also see the consequences of our withdrawal in less catastrophic terms than most critics of the move.

As I noted not long after it was concluded, the Paris Agreement is by design much weaker than its predecessor, the Kyoto Protocol. Although the 2015 Paris deal was probably the strongest one that could have been negotiated at the time, it still represented a big compromise between developed and developing countries on who should reduce the bulk of future emissions and who should bear the responsibility for the consequences of past emissions. Its text is full of verbs like recognize, acknowledge, encourage, etc., and the commitments it collected were essentially voluntary.

The agreement was also explicitly negotiated so as to maximize its chances of being enacted under the executive powers of the US president, without his having to refer the agreement to the US Senate for its concurrence. That implied it could be undone in the same way.

In other words, President Obama took a calculated risk that his successor(s) would choose to be bound by his Executive Order endorsing Paris. That was tantamount to a bet on his party winning the 2016 election, since most of the Republicans who had announced at the time were opposed to it, or the Clean Power Plan that was the linchpin of future US compliance with it.

Seeking Senate approval as a treaty would have been a much bigger lift--or required an even weaker agreement--but success would have provided significant political protection for the follow-on to the unratified Kyoto Protocol. Perhaps that explains why President Trump has chosen the much slower exit path--up to three years--provided within the Paris Agreement, rather than the quicker route of pulling out of the umbrella UN Framework Convention on Climate Change. The Convention was signed by President George H.W. Bush with the bipartisan advise and consent of the Senate in 1992.

Federal climate policy has not been the main driver of recent emissions reductions in the US power sector. Cheap, abundant natural gas from shale and the rapid adoption of renewable energy under state "renewable portfolio standards", supported by federal tax credits that were extended again in 2015, have been the primary factors in overall US emissions falling by11% since 2005. These trends look set to continue.The bigger question is what happens globally with the US out of the Paris Agreement--assuming the administration does not reverse course again before it can issue the required formal notice to withdraw roughly 2 1/2 years from now. At least in the short term, I doubt much else will change. For the most part, the Nationally Determined Commitments delivered at Paris reflected what the signatories intended to do anyway. China's NDC is a perfect example. That country's ongoing air pollution crisis provides ample incentive to scale back on energy intensity and coal-fired power plants, which are the main source of its emissions. Increasing the role of renewable energy in its national energy mix perfectly suits China's ambitions in renewable energy technology. Exhibit A for that is a solar manufacturing sector that went from insignificance to more than 50% of the global supply of photovoltaic (PV) cells in under a decade, while China's domestic market accounted for 21% of global PV installations through 2015. The reactions to last week's announcement surely raised the stakes for other countries that might consider leaving. However, this action has also provided China and other high-emitting developing countries with an ironic mirror image of one of the main arguments on which the US government based its unwillingness to implement the Kyoto Protocol. What ought to matter more than any of the domestic and geopolitical maneuvering around the US exit is the actual impact on the global climate. Reporting on Axios, Amy Harder (formerly of the Wall St. Journal) portrayed this as a sort of emperor's clothes moment with a column entitled, "Climate change is here to stay, so deal with it." Monday's main Axios "stream" characterized her piece as a "truth bomb." As Harder put it, "The chances of reversing climate change are slim regardless of US involvement in the Paris agreement." That's consistent with recent assessments from the International Energy Agency and others. Citing the Bipartisan Policy Center and the UN, her column suggested a pivot to greater focus on adaptation, the hard and deeply unglamorous work of bolstering infrastructure and systems to withstand changes in the climate, including those that are already baked in. Attributing the source of changes in rainfall and sea level matters less than plugging the resulting physical gaps. That makes adaptation politically less toxic than cutting emissions, though still plenty challenging, fiscally. As I have been watching the fallout from last week's news, I keep coming back to comparisons to the Cold War that I made when the idea of pursuing climate policy through executive action was emerging in 2010. Like the Cold War, dealing with climate change requires a similarly enduring bipartisan coalition. Major policy swings every 4 or 8 years are just too costly and ineffective, due to the planning horizons involved.NATO may be going through a difficult moment, but it is approaching its 70th year. After seeing its key weakness exposed, can anyone honestly look at the framework of the Paris Agreement and conclude that it is likely to last as long? Yet if climate change is as serious as many suggest, those are exactly the terms in which we should be thinking.